One type of display panel which has been made and sold commercially is known as a SELF-SCAN panel and is described in many patents including U.S. Pat. No. 3,989,981, dated Nov. 2, 1976, of James A. Ogle and George E. Holz. A version of this type of panel, known as a SELF-SCAN I panel, includes two layers of cells, a lower layer of scanning cells, and an upper layer of display cells, with each display cell in operative relation with a scanning cell. Another version of this general type of panel has the scan cells and display cells coplanar, and is known as a single layer panel, or as a SELF-SCAN II panel. This panel is described in U.S. Pat. No. 4,099,098, dated July 4, 1978, of Rudolph A. Cola. Another single layer panel is shown in U.S. Pat. No. 3,631,530, dated Dec. 28, 1971, of James A. Ogle, and the present invention represents an improvement in the keep-alive mechanism for the panel described in the latter patent.